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P0966 OBD-II Trouble Code: Pressure Control Solenoid B Control Circuit Low

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P0966 code definition

P0966 is the fault code for Pressure Control Solenoid B Control Circuit Low, indicating a problem in the system which controls the pressure in the automatic transmission clutch. Concurrent codes may include P0968, and P1773.

What the P0966 code means

This code typically means there is a problem related to the pressure control solenoid valve, which determines the flow and pressure of transmission oil according to driving conditions. This results in the vehicle’s computer detecting voltage outside of the normal range.

What causes the P0966 code?

Several possibilities could cause a vehicle to set this code, including:

  • Open or short in the pressure control solenoid valve B harness
  • Bad connection in the pressure control solenoid valve B circuit
  • Hydraulic system malfunction
  • Bad pressure control solenoid valve B
  • Dirt or debris in the transmission fluid, or insufficient fluid

While mechanical problems can cause this DTC, the issue is more often electrical.

What are the symptoms of the P0966 code?

The most common symptom is an illuminated Check Engine Light. The vehicle may also have problems shifting gears, such as harsh upshifts, or flares or shock upon upshifting. If there are downshifting abnormalities, that is more likely a sign of an issue with the pressure control solenoid A. You may also notice decreased fuel efficiency.

How does a mechanic diagnose the P0966 code?

A technician may carry out the following diagnostic steps:

  • Capture any freeze frame data and other codes the computer has set
  • Clear out the codes to check if they recur after road testing the vehicle
  • Monitor the vehicle’s computer on a scanner while driving in order to observe the data
  • Measure the resistance and voltage between the pressure control solenoid valve connector terminals
  • Inspect the wiring and harness for a short or open
  • Inspect the connection between the PCM and the solenoid valve

Common mistakes when diagnosing the P0966 code

One of the costliest errors with this fault is to replace the transmission without checking all of the other possible issues. This code is rarely caused by a mechanical problem with the transmission. The wiring harness is a frequent culprit. The problem may also lie in the ECM or PCM – if a used computer has been installed in the vehicle, it may be storing the code despite the lack of a malfunction. In addition, this DTC is sometimes mistaken for a performance problem.

How serious is the P0966 code?

While the problem is often electrical, this DTC can result in very real transmission malfunctions. If not addressed so that the proper fluid pressure can resume, the transmission could eventually be damaged to the point of needing to be replaced. It’s best to address the code as soon as you see that it has set.

What repairs can fix the P0966 code?

Possible solutions for this error include:

  • Replacing pressure control solenoid valve B
  • Repairing or replacing damaged wiring or harness
  • Tightening loose connections between the solenoid valve and the PCM
  • Flushing the transmission line and replacing the fluid
  • Updating the PCM software
  • Replacing the PCM (rare)

Additional comments for consideration regarding the P0966 code

If the code does not return after being cleared from the computer and car road tested again, it could indicate an intermittent failure. These can be difficult to diagnose and may require allowing the code to set consistently before it can be addressed. You should always check for loose connections if there appears to be an intermittent failure.

It’s important to get a correct diagnosis for codes relating to the transmission, because if not properly repaired, serious transmission damage could result. Special equipment is often required to test voltage and resistance, and to verify the source of the problem, so this is one repair that is usually best left to a professional technician.

Need help with a P0966 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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